Flying machine



June 22 1926. I

, C. A. WRAGG FLYING MACHINE Filed' Nov. 27. 1918 2 Sheets-Sheet l 5 11 we, 1:1 foz I I 'v me/b June 22 1926.

C. A. WRAGG FLYING MACHINE File Nov. 27. 1918 2 Shets-Sheet 2 am w 11 toz 64 44 M .Ah

t "if I Patented June 22, 1926.

PATENT OFFICE.

UNITED STATES FLYING MAcn'tnE.

Application filed November 27 1918. Serial No. 264,365.

This invention relates to certain improvements in flying machines and refers more especially to machines heavier thanair, tho it will be understood that the invention is equally applicable to lighter than air machines, such as dirigibles having project-- ing planes or vanes.

So far as thescience of aviation has advanced'at this'time, the general principles involved in the construction of aerofoils are well understood, and thus we have biplanes .and triplan'es with wings whose chords, cambers, and ratio of chord to span follow wellknown formulae, whereby assured. results are attained. Enlargement of these supporting surfaces, however, is impracticable beyond certain limits, the use of wings with very low drag values is difficult, and the general development of individual wings has about reached a limit.

In order further to improve the efliciency and liftingcapacity of the supporting surface, my conclusion is that a compound aerofoil must be devised by the production of proper sections and by properly arranging them one behind another, not in true tandem but in a manner to be described, and accordingly, an object of this inventionis to enable aerofoils to be efiiciently set in their relation to each other in order to provide such a compound aerofoil for the purpose of enabling airplanes to be designed having a larger area than at present with. improved speed and landing capacity.

In the drawing Fig. 1 is a diagram showing an end view of my compound aerofoil as applied to an airplane;

Fig. 2 is a detail diagram showing more in detail the relation of the two sections of the aerofoil;

Figs. 3, 4:, 5 ad-fi are diagrammatic views showing forms of my apparatus in which the rear sections are arranged to be tilted;

Fig. 7 is a diagram showing the manner in which the air currents are taken advantage of in my compound aerofoil; and

Fig. 8 is a diagrammatic view showing a mechanism for simultaneously shifting the movable parts of the aerofoils in a bi-plane. It is well-knownthat in combination of wings in which rear wings are :set'in a direct line longitudinally with the leading wings, the efficiency of the rear wings is much reduced. ItIis also known that in superposed -wings,-the general effic ency s .It will be observed from my reduced. I have discovered :thatif wings are placed so that one wing is so far staggered 1n relation to another as not to constitute a substantial or true superposed arrangement and so far below the tandem position as not to constitute a true tandem arrangement (see sections A and B in Fig. 1 and Fig. 8,) and if the lifting value of the rear section is less than the lifting value.

of the forward section, (as-also shown in said figures) and their curvesfaired for' mutual action on the same airstream then an aerofoil is devised the rear section of which is in the most advantageous position for a compound'or cooperative relation with the front section.

It is desirable in high-speed machines that the wings should have a cross-section or camber which gives a low lift-coefficient and a high efliciency at low angles; and as it is also advantageous to group the weights closely and to concentrate the surface area as much as possible, vention is to enable win'gs used in close proximity in order to increase the carrying surface for large airplanes. drawings that this is done by choosing sections or camber for the com ound which have a low lift.- coeflicient an a high efliciency at low angles. The, term low lift-coeflicient or low liftvalue as distinct from a hi h lift-coeflicient at given angles is taken to ie, in this specification, inclusive of the lift-values which do an object of this into be efliciently not cause the efliciency of the compound to 1 fallv off so much as to make the compound non-useful.

The airflow immediately following a wing set at an angle of incidence has a general downward direction, but this is very gh speed with slight at low angles, and at hi efficient high-speed sections, 1. e., sections having a low lift coeflicient, t ere is a reactionary upward tendency of the airflow due to the pressure'on the lower surface being sudden y released and to the read'ustnient of the differences in the density .0 the air above the upper surface of and immediately under the lower surface 0 the 'aerofoil caused This adjustment of the two the aerofoil by the aerofoils passage through the air.

different atmospheric densities is completed a at .some distance tothe rear of the aerofoil and causes a general disturbance of the air in a particular region. I have found by wind tunnel tests that a rear wing of less liftin'g powerhaving'convex upper surface placed as described reduces the eddies, which represent dissipated energy, and improves the entire airfiowover the whole of the front wing, showing av most extraordinary compounding effect. It necessarily follows from this that the efliciency can lie-improved v by reduction'of drag andincrea'se of lift. Moreover, if the lifting value of the rear section is less than; the hft of the forward section, thus allowing the center of gravity to be situated further forward, an inherent stabilizing tendency is embodied in-the aero- 'foil system,-amounting in effect to a longitudinal dihedral angle or V between the angles of zero' lift ofthe forward'and rearward sections, respectively, Referring to Fig. 2. 1t willvbe' seenthat 1f; the center of pressure'on each section is at-a and a, re

spectively, and ifthe-lifting valueof each.

is equal, thenthe cehter ofpressure of the compound would be midway between the two moments, as shown at I). But if thev total lift on section B, due'to difference in section or area or section and area, is less than the lift on section A, then the center of pressure of the compound (and of coursethe center of gravity) could be situated. farther forward. to some point'asshown at 0, because the product of each'of thepres sures and its distance from the center of gravity, or, in other words, the moment of each pressure in relation to I p the center of gravity, should be ,the same. air disturbance tilts the whole airplane about an axis passing through thejcenter of gravity, the rear section B 'reaches its angle lever-arm at- 0)- is arighting'one inboth w cases.

The va-lueof' the lift on section B as compared with the lift of section A and their relation to the variations of the center" of I pressure on section A are some of the factors which determine. the position of section 1 B in relation tosection in the compound," A-

pound. i

pounding'to take advantage the-airflow from the leading wing and of somewhat similarreasoning applies if the difference, in lift on the sections is "obtained by making them difierent in area instead ofdifferent in section.

The section and the,- area of wing B- may -be different from that of wing A for the purpose-of securing .t-hemost efficient coni- 'coin'cidenfl'y of the stabilizing factor introduced .by the com- The speed-of airplanes isinter alia govowed by the lift coeflicient of the aerofoils,

caselost by and the lower the valueof the lift, other fac tors remaining constant, the greater the speed. One'of the limitations to greater speed is the dificulty of utilizing lower lift-value wings with safety and stability. The introduction'of the stabilizing fact-or inherent in .this compound aerofoil enables the use 'of' sections having lower lift value at, their angle of maximum etficiency and enables them'to' be set at lower angles of incidencethan hitherto. Thus both sections couldbe set with their chords at zero angle ofincidence in relation to the'horizont-a-l axisof themachine, each section having a different angle of zero lift and a maximum or high efliciency at the zero angle of incidence of chord.

' If thestabilizingfactor herein: referred to isnot desired in some machines of this type.

the sections can be made similar withoutdeparture. from this invention, providing' each. sectionis of the efficient high-speed type previously herein described. I have observed that when sections are successively modified in their cross-section curves so that lower angles and the lift coe cient. made .90 the point of maximum eificienc occurs 'at' I lower-at given angles, the tendency is for the maximum point'on the efiiciency curve to be higher in some cases, and part of my invention isthat if such sections are used an efiicient closely-grouped arrangement is pos-. sible because both wings' :when"integrated into a 'faired or compound-structure is to' direct thcairstream into a so-called streamline 'flow,. i. e.,

eddies.

The increasedareaiby reason'of section-B. being added to section A "enables greater maximum speed.

weight to :be carried at v Iii-Figs. different ways of .obtai ning an angular adjustment of the rear or trailing section, In each of these cases, therear section is pivoted .on' a. horizontal axis extending transversely of the;line offlightand-arranged in such relation tothe forward section that when its forward edge istilted-upwardly,gsaid forward edge will approach or 'meet the I 'rearfledge- 'of'the'iforwa-rd section, so that 1 the upper surfaces'of the-two sections will The object of be substantiallycontinuous." this-is to'increase the'total lift for the-pun pose of landing slowly. It will be understood that;when' the-rear section isswung to said position; I lose entirely the aerodynamic .h-igh speed,- but this efl'ect would be in any for landing.

My compound aerofoil may be used inzmar chines of a monoplane type,--or it maybe arranged inseries, such as one or several su-- perpose-d above another or in tandem or in one in which little or no energy is lost in.

thelefiect of each element of 3,4,5 and 56 I show in diagram advantages of 'the compounding effect at thereductionin'speed necessary .125

any of the formations in which single aerofoils are arranged.

In Figs, 3 and 5, it will be observed that the axis'of oscillation is at 7", a point within the body of the section, while in Figs. 4 and 6 the pivotal point is at f, a point above the body of the section. In Figs. and' 6, the tapered trailing portion h of the forward section is hinged to adapt it to be adjusted downwardlyto approach the front edge of the rearsection. The tilting or oscillation of the rear section on the pivot f or f may be manually brought about by any suitable devices.

In the drawing, the rear section is of less lift-value by reason of; the fact that its un-' der side is convexed while the under side of the forward section is horizontally flat, but it will be understood, as hereinbefore stated, that the lower lift-value of the rear section may be provided for, in any other suitable manner,

- It will be observed from the foregoing to enable higher speed to be attained, and another is to enable greater weight to be carried. As with a given area and loading a high value .of lift in the aerofoil is detrimen- 3 tal to high speed, and as with a given speed mental to large weight-carrying capacity, the exact cha-racterjofthe upper and lower cambers used in each section of my compound aerofoil and the exact position of each section in relation, tothe other are influenced by the particular objective in the mind of the designer. -The sections and their relative position can be principally determined by the necessities of very high speed, vor'by large weight-carrying, or by a compromise for both, the sections being designed and compounded by fairing one with the other through the cooperative alinement of. their surfaces as herein specified, to mutually affect each other most advantageously for the particular objective by reason of certain laws of physics and mechanics. These \laws are of such a nature that if sections having a high lift coefficient were used in the compound the efficiency of the compound would fall off to such an extent as to make the device non-useful, but if the aerofoil is composed of sections having a'sufliciently low value of lift and drag coefiici'ent-that a low value of lift and low area are detri is. approaching the symmetrical in form-it 'tionary upward airflow. or plus density, thatv indicated as being within the zone of reacis, with its leading edge not farther back v than a chord length from the trailing edge of the forward section, nor-farther down in a vertical direction that half the chord length of the forward section. It will be seen also that this reactionary flow of the air at very high speed from the lower surface of the forward section assists in augmenting the evenness of fiow and the rarefaction of the air above the upper surface of the rear section.

It will be understood that the foregoing desirable results may not be obtained in the most highly desirable degree at low speeds where the air currents may not be in the matter of direction exactly as'shown in Fig. 7 as the nature of the airflow varies when there is any very great difference in speed,

but there can be no question as to the correctness of the theory outlined where the higher speeds now demanded are attained. that one object of my compound aerofoil is.

a In Figs. 5 and 6, the trailing portion h of the forward section is made angularly ad-l of the aerofoil for landing.

For simultaneously shifting the balanced rear sections B as well as the trailing portions h of the front sections of a bi-plane, I

useful. The airflow about the compound is diagrammatically illustrated in Fig. 7, in

which the forward edge of the rear section is may use the mechanism shown in Fig. 8, in which the two rear sections are pivotally connected by an upright rod 5 and the upper section is connected at opposite sides of the pivotal point f by cables j to a lever is, while the pivots f of each of the sections B are connected by link-wires Z and arms m to the pivots of'the trailing members h, so that by oscillating the lever hon its pivot n all the pivotal members B and Z1 may be simultaneously angularly adjusted either upwardly or downwardly to eitherentirely or only partly close the gap between the aerofoil sections.

It will be seen that the adjustment of the rear wing to vary thesize of space between the sections will vary the angle of incidence of the entire aerofoil and thus will allow the aeroplane to have a range of speed between that provided by the camber of the individual sections and the camber of the closed system or compound.

The usual individual suction value on the upper surface near the leading edge over about one-third of the chord and dropping off very rapidly towards the trailing. edge. The effect of'the rear wing in my compound however, is to increase the suction over the remaining two thirds of the surface without'causing the advantage gained to be lost gain y the pas aerofoil gives ahigh the airstream in the path of least dissipation of energy. Further, since this greater efficiencyis obtained with the wings in close proximity, it willbe seen that my compound sage of'theair over itself, making a more uniform distribution over the whole aerofoil as exemplified by stability while testing for lift and drag and also in pressure distribution tests. This uniform distribution of pressure is an assurance of stability.

It will be observed that. a feature of importance in my airplane is that the forward wing'shall have its maximum efficiency ocour, at low angles for best results, and in Fi underside is flat while the upper surface is famed to reduce vortlces to a minimum, wlule producing lift; this type of wing producesv results in compound-not to be obtained by the deeply concaved' wings used in disclosures of closely grouped systems which have equal chords. But it will be understood that other shapes of under surface may be used in my apparatus, provided all the elements of the surfaces of both wings are made integral and their chords proportioned to direct wring is not only an aerodynamic improve?- ment but has structural advantage in-that the structure of my apparatus compares favorably with that of an ordinary wing. I The nature and scope of the invention having been thus indicated and its preferred ernbodiment having been specifically described,

- wings normally disposed in substantially parallel separate planes,

2. A compound wing composed of dissimilar wings set close one behind the other with a-gap between, said wings acting on the same airstreams, the rear wing having less 2 I show a cross-section in which the same.

thanhalf the chordand thinner cross-section than the forward wing, said rear having its upper andlower surfaces convexed and compounded with the curves of said forward wing to reduce eddies in the said air-streams and embody inherent stability as described, said wings being normally in substantiallyparallel planes.

which said main .wing and said auxiliary wing have substantially equal span.

.3. The structure according to claim 1, in I 4. The structure according to claim 1, having means for desired. v

- 5. The structure according to claim 1, havclosing the gap to the extent ing therear wing pivoted .so that it may tilt to vary the angle of incidence.

6. The structure according to claim 2,.

having means to reduce said gap in accordance with changes in load and for landing. 7. The structure according to claim 2, hav ing the leading edgeof said rear wing in adwing. p 8, In a compound aerofoil, a, pair'of wing Vance of: the trailing edge of said forward.

sections set one behind and below the other with a gap between, the lower surface of the forward wing being non-concave, at the trailing portion, said'wing sections being set sufficiently close to mutually affect the airflow immediately above and below their sur faces, said forward Wing being provided with a hinged trailing portion adapted to swing .vertically so as to vary the extent of opening between the two Wing sections.

9. A flying machine in which the wing is composed of two sections arranged one behind and below the other, characterized by the forward section being provided with a vertically-swinging trailing portion and the rear section being mounted pivotally on an axis extending transversely of the line of flight, and means for simultaneously shifting said rear section and said trailing portion to:vary the extent of gap between the In testimony whereof- I' hereunto aflix my signature.

CHARLES ARTHUR WRAGG. 

